If you have an autoregistered host (monitored by proxy), initially registered without "HostInterfaceItem", and only an IP interface is present, then everything is working as expected.
When you add a "HostInterfaceItem" parameter, the same interface gets a DNS name added, and "Connect to" main connection is set to DNS, as expected.
Afterwards, if "HostInterfaceItem" parameter is removed from Agent2 configuration, a duplicate IP interface is added, and not even switched to be the default one. The first interface is kept as the default one.

STEPS TO REPRODUCE:
1. Set up a simple autoregistration action:

2. Configure Agent2 to connect to a proxy
3. Configure Agent2 with "HostMetadata" parameter:

4. Watch the host be created in Zabbix:

5. Configure "HostInterfaceItem" parameter to have value "system.hostname":

6. Hosts interface is updated to have a DNS connection:

7. Remove "HostInterfaceItem" parameter from Agent2 configuration
8. Watch the host have a "duplicate", useless interface be added:

EXPECTED:
The first interface should switch "Connect to" to IP, and perhaps remove the DNS name configuration from the same interface, instead of adding a new one, which is not even set as default interface.
No second interface should be added.
In such a scenario Zabbix loses connection to the host, because host is no longer reachable using DNS name , but the DNS interface is left as the default one, even though a secondary interface with IP address is added.